Measuring and control apparatus



July\14, 1942. w. P. WILLS 2,289,947

MEASURING AND CONTROL APPARATUS Filed June 22, 1938 ATTORNEY,

I Pa tented- Muir-so" r STATES! ;rarsa'r MEASURWGANDOONTROL APrnna'rus Wills, Philadelphia. Pa assignor to The Brown Inatrument Oompany, Par, a corporation of Pennsylvania application lune 22, 1938; Serial N zi-5,127-

' Walter P.

ACIaima' This invention relates to electronic control cir cults. r The present invention is a continuation in part of my prior application Serial No;159,8'75, filed August 19, 1937, for Control'apparatus, now Pat-- ent No. 2,256,304, September 1-6, l941,-which'dis-' closes various arrangements of an electrical control instrumentality of the kind which may be used to control the application of a quantity in response to fluctuations of a variable condition to maintain the condition constant.

A specific object of the present invention is to provide an electronic ,lcontrol circuit which is especially adapted for uhe in a system of the type referred to, and is relatively simple in construction' and may be operated from a commercial alv ternating current supply source without the use of transformers and power rectifiers.

l A more specific object of the present invention is toprovide an electronic control circuit which is sensitively responsive to minute alternating voltages and will, amplify and 'translate'all frequencies. over a wide range of frequencies into a 4 direct current ,potential which may be employed to eflect acontrol operation. A

A still more specific bject of the present invention is to provide? 11 electronic control circuit of the type referred tively small capacity filtering means may be employed in a network for deriving from a commercial source of alternating current voltage a sourceof direct current voltage, which is substantially constant in value and free fromrlpple current effects. y

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a Fig. 2 is a perspective view of a portion of the I is employed for setting the mechanical zero of the galvanometer arrangement of Fig. 1 which employed in -that arrangement;

Fig. 3 illustrates a modification of the ampliv fler shown in Fig. 1;

Fig. 4 illustrates a modification of the arrangeto above in which rela-- specific objects obtained with its use,

Philadelphia,

ment disclosed in Fig. 1 including means for modulating the heat input to the furnace; and

Figs. 5 and 6 illustrate modifications of a portion of the arrangement of'Fig. 4.

5 InFig. l of the drawing, I have illustrated, more or less diagrammatically, a furnace or. other compartment to be heated at I in which an electrical heating element 2 is arranged and adapted to be supplied with energizing current from sup- 1 10: ply conductors 3 and}. A thermocouple E, which to variations in tem- :is sensitively responsive perature, is mounted in the furnace I and has its terminals connected by conductors 8. and to the terminals of a deflectional potentiometric 'v measuring network 8 at a point remote from the -furnace i.

The potentiometer network} may be of any suitable type such as the Brown potentiometer circuit disclosed in the Harrison Patent 898,124- issued February 21 1933, and for the present purposes it is sufficient to note that thepotentiomef'ter circuit 8 includes a circuit branch comprising including a source of known potential, such as a battery 9 and a pair of resistors i0 and H, a variable portion of which may-be connected into the opposed branches by means of a sliding'contact i2 whereby the respective efiects of the variable and the knownsources are made equal and opposite. Differences in the variable and known I sources of potential are adapted to be. detected by. a galvanometer E3, themoving coil i l of whichis connected in the circuit branch including the thermocouple 5, so that when the variable and known sources of potential are equal and opposite the galvanometer moving coil will be rendered undeflected when the circuit is balanced for a.

predetermined value of the E. M. F. of the thermo'couple with the contact I! in a correspond- 40 ing position along the slidewire resistors l0 and II. a

As illustrated the moving coil It of galvanometer i3 is connected in the conductor- 6 by means of slip rings l5 and i6, and a pick-up coil i1 is connected to the pivot of the galvanometer moving coil. The pick-up coil i1 is positioned between the poles of a fleld structure l8 having a field winding l9 which is adapted to be energized from the alternating current sup-' ply lines L and 1?, and is preferably, althoughnot'necessarily, so arranged that when the galvanometer is in its undeflected position the pickupcoil will be slightly in inductive relation with the alternating magnetic field set up by'the field structure. 7 The extent to'which the pick-up coil 4 orifi e l the thermocouple 5, an opposing circuit branch n is in inductive relation with this alternating magnetic field and the manner in which the ad- .justment may be efiected is described hereinafter.

For facilitating the adjustment of the instrument to control the temperature of the furnace at .the desired value the potentiometer sliding contact l2 may be mounted on a contact arm which desirably is arranged in cooperative relation with a suitably calibrated scale;2| and is through the galvanometer moving coil M. The

galvanometer moving coil thus energized will defiect in a corresponding direction and rotate the pick-up coil I! to a new position between the poles of the field'structure l8.

The alternating voltage induced in the pick-up coil I! from the field created by the winding I3 is connected by slip rings 23 and 24 and conductors 25 and 25 to the input terminals of -an electronic amplifier. 21 which is employed to amplify the induced voltage and the amplified quantity is employed to control the energization of a suitable relay 23 into its open or closed position.

The amplifier 21 illustrated is especially desirable in a system where simplicity, compactness and ease of construction are essential features for, as will be described it may be operated directly from the alternating current supply conductors L' and L and does not require the use of power rectifiers or transformers. As shown,

the conductor 25 is connected to the control grid' 33 of an electronic valve 29 and the conductor 26 is connected to the cathode 3| thereof. The valve 29 is a heater type triode and includes an anode 30, thecathode 3|, a heater filament 32, and the control grid 33. The heater filament 32 is adapted to receive energizing current from the alternating supply conductors L and L and is connected in a series circuit thereacross which includes the heater filaments 31 and 43 of a pair of electronic valves 34 and 40 and a pair of resistors 45 and 41. It is noted that this circuit in efiect comprises a voltage divider from which various potentials may be tapped to supply energizing voltages to the valves 34 and 40.

The valve 34 is a heater type duplex-diodetriode and includes an anode 35, a cathode 36, the heater filament 31, a control grid 33 and a pair of diode plates39, and'the valve 49 is a 'tetrode preferably of the type known commercially as beam power amplifier tubes and includes an anode 4|, a cathode 42, the heater filament 43, a control grid 44, and a screen grid 45.

As will become apparent the valve 34 is employed to supply direct current voltage to the anode circuit of valve 29 and also to further amplify the amplified quantity of the voltage induced in the pilot coil II which is impressed ngon' the input circuit thereof by the valve 2 Anode voltage is supplied .the valve 29 through a circuit which utilizes the rectifying action of the diode plates 39 of valve 34 and ductor 52 to one terminal of a condenser 53 which constitutes the positive side of a half wave rectifying' unit. The condenser 53 has its negative of condenser 53 through a resistor 55 and the cathode 3| is connected to the negative side to permit the use of a small filtering condenser 53, the valve 291s preferably operated with the cathode 3| 7 virtually cold and with a relatively low voltage on the anode circuit. The temperature of the-cathode 3| may conveniently be kept at a low value by shunting the heater filament with a resistor 55 so that the filament heating current will be small, and it will be apparent the potential on the anode 39 may be adjusted to a desirable value by properly proportioning resistor 46. Thus, by so adjusting the anode to cathode resistance of valve 29, it will be readily apparent that the discharge of current through the valve 29 by the condenser 53, during the half cycles when the diode plates 39 are negative, may be reduced to a negligible value and thevoltage maintained on the anode 30 may be maintained at a substantially constant. value. It. is noted that this method of increasing the anode to cathode impedance of valve 29 is advantageous over the well known method of applying substantially constant potential drop will be maintained across the resistor 55. When ,the pick-up coil is deflected in one direction or the other from its neutral position, however, it is noted an alternating voltage in phase with or 180 out of phase with the line voltage will be impressed on the input circuit of valve 29, and the latter will then be alternately rendered more conductive and less conductive resulting in a pulsating direct current fiow through resistor 55 and .thereby in a corresponding pulsating potential drop across the latter. a

The positive end of resistor 55 is connected to the cathode 36 'of valve 34 and a connection is also provided between this end of resistor 55 and the control grid 38 which includes a resistor 51. As shown a condenser 53 is connected in shunt to the resistors 55 and 51 and it will be apparent that when a steady flow of current is conducted which may be traced from the supply conductor L'- to a conductor 43, conductor 49, heater filament 3-1, a conductor 59, resistor 41, a conductor 5|, the diode plates 39, cathode '36, and a con by valve 29 a charge will be stored on the condenser 58 which is equal and opposite to the potential drop across resistor 55 whereby the potential drop across resistor 51 will be zero and the control grid 39 will have the same potential as the cathode 36.

When an alternating voltage is impressed on the input circuit of valve 29, however, a pul- -slstor 33 and accordingly the condenser 53 will lalternately charganddischarge through the resistor 51 to produce a fluctuating potential drop across-the latter, and it will be noted this potential drop will be impressed on the input circuit of valve 34. I

Anode fioltage from the alternating current supply conductors L and Ii -through a circuit which may be traced from the supply conductor L, conductor 43, conductor 43, heater filament 31 of valve 34, con-' ductor 50, a conductor 33 in which a resistor 30 is inserted, anode 35, cathode", and conductor 33 to the positiveterminal oi condenser 53. Thus,

the anode circuit 01 valve 34 is completed through the parallel arrangement consisting of the anode circuit oi. the valve 29 and the condenser 53, and it is noted themagnitude of the pulsating current conducted by valve 34 is adapted to be varied I diode section of valve 34 should preferably be made many times as large as the current conducted by the anode circuit thereof. Or in other words the diode'plates 39 of valve 34 should be connected to a point on the voltage divider of suchpotential that the potential of the cathode 33 will be determined primarily by the current conducted in the circuit including the diode plates 33 and the cathode 3B. i

The obvious mannerof rendering the current conducted by the diode section of the valve predominant indetermining the potential or cathode 36 would be to connect the diode plate 39 direct to the supply conductor L, but it is noted hat ifthis is done the voltage available for the anode circuit of valve 34 will be insumcient. Thus, the diode plates 39 must be connected to a point on the voltage divider of such potential that the current conducted by the diodes will be predominant in determining the po tential of the cathode 3G and in addition that there will be suflicient voltage available for the anode section of the valve 34.

--When a fluctuating potential is impressed on the input circuit of valve 34,'tl is valve willbe rendered less conductive or more conductive during the half cycles when the anode 35 is positive depending upon whether the voltage impressed on the input circuit thereof is in phase or displaced 180 in phase with the alternating voltage applied to the anode, and accordingly the current flow through resistor 60 will be varied to a corresponding extent. Inorder to smooth out 'the pulsating current flow through'resistor 60 a condenser 6| is connected thereacross, and as will be apparent a potential drop will then be produced across resistor 64 which 'will gradually .rise when an alternating-potential in phase with "the supply linevoltage is impressed on the inputcircuit of valve 34 until a condition of equilibriurn is reached and which will gradually fall to a'lower value when an alternating voltage 180 out of phase with the supply line voltage is ima pressed on the input circuit of valve 34. Thus, a negative'potential is built up'on the anode 35 which is adapted to be varied as'the pick-up coil l'l deflects in one direction or the. other from its normally balanced position and as will becomeapparent this negative potential may desirably sating'potential drop will appear across the reis supplied the valve 34 directly I be employed to control the conductivity of valve by way or illustration it is noted that when the I voltage of the supply conductors is 1' vo he valve 29 may be of a type known commercially as a 6P5 type, the valve 34 may be a type 6Q7, the

' n ay'be as-follows:

Part Value 100 ohms.

175 ohms. l megohm.

1 megohm.

.6 microiamd. .05 microiarad. .05 microfarad.

As illustrated the anode circuit of valve 40 is connected in an inverted position across the alvalve 40 may be a type L6, and correspondingly suitable values for the various circuit constants ternating supply conductors L'- and I? with respect to the manner of connection pf the valve 34 thereacross so that the valve 40 will be nonconductive during the half cycles when the valve 34 is conductive, and conductive when the valve 34 is nonconductive. Due to the action of condenser 6|, however, the potential drop across resistor fillwill persist during the, half cycles when the valve 34 is non-conductive and may, there- 'fore, be employed to control the conductivity of valve 43 which is conductive during these half -cycles. As shown the negative end of resistor I 60 is connected by a conductor 62 to the control grid 44 of valve and the positive end of resistor 60 is connected by means of conductors 59 and 50, the heater filament 31 of valve 34, and conductors 49 and 48 to. the cathode 42 so that the potential drop across resistor 60 will be im-. pressed on the input circuit of valve 40.

Anode voltage is supplied the valve 40 through a circuit which may be traced from the supply conductor L a conductor 63 in which a milliam- The screen grid 45 is desirably maintained at a potential which is somewhat lower than" the potential applied the anode 4| and may be connected to the point of connection of resistors46 and 41.. i l 7 Thus the valve 46 is adapted to be alternately rendered conductive and non-conductive and the amplitude of the pulsating current conducted thereby is adapted to be controlled in accordance with the direct current potential drop across resisi or 60. In order to smooth out the pulsating current flow through the relay 28 and the milliammeter 64 'to thereby prevent chattering of the relay and to facilitate reading of the milliammeter, a condenser 65 is preferably connected across these units.

It is noted that when the. above values for the ' matched electronic valves are employed, an automatic compensation for line-voltage fluctuations is obtained wherebyv the current flow through revalues'of the various circuit components, particu larly adjustment of the resistance of resistor 60 various circuit componentsare used and suitably meter 64 and the relay 28 are inserted, the anode 4|,and cathode 42 to the supply conductor L.

line voltage increase.

and relay 28 and the point of connection of screen grid 45 of valve 40 along resistors 46 and 41.

In the. circuit arrangement illustrated, a line voltage change tends to vary the anode current of valve 40 in much the same manner as that current is varied by deflection of pilot coil I! from its normal position, but such change in line voltage may be precisely compensated for in a manner to be explained. This compensating action is obtained by virtue of the fact that if the line voltage should change, increase, for example, the conductivity of valve 34 will increase to produce a greater voltage drop across resistor 60, and this increase in biasing potential across the latter will exactly offset the tendency of valve 40 to conduct a larger current as a result of said I have found, in practice, that when the electronic valve characteristics and the circuit constants have been suitably proportioned, the line voltage may 'vary as much as 20% in either direction from an intermediate normal value, for which the apparatus is designed, without resulting in significant change in the anode current conducted by valve 40.

An armature 66, which is shown pivoted at a point 61 and gravity or spring biased for rotation in a counterclockwise direction into engagement with a stop 68, is arranged in cooperative relation with the relay 28 and is adapted to be rotated in a clockwise direction into engagement with the relay core when the relay is energized. The armature 66 may be formed in the shape of a right angle and the point 61 at which it is pivoted may conveniently be at the bend. One arm is directed in an upward direction .and is adapted to move between the stop 68 and the relay 28, and the other arm which is adapted to be moved about a horizontal position carries a mercury switch 69. The mercury switch 69 includes contacts which are adapted to be closed when the armature 66 is in its extreme clockwise position and to be opened when the armature is in its extreme counterclockwise position as shown.

As illustrated the contacts 10 are connected in 'a circuit including the heating resistor 2 and the power supply conductors 3 and 4 so that when the relay 28 is energized the mercury switch 69 will be actuated into its closedbosition to close an energizing circuit to the resistor? Thus, as the temperature of the furnace l rises, above or falls below a predetermined value at which it is desired to control the temperature, the mercury switch 69'will be actuated to its open and closed position accordingly to thereby cut off or supply more heat to the furnace! As was mentioned hereinbefore, Icontemplate two modes of operation for ,my control system.

In accordance with one method I contemplate operation in which the pick-up coil I1 is normally slightly in inductive relation with the magnetic field set up in the field structure l8 and in which,

the phase of the induced voltage is not changed as the relay 28 is actuated to its open and closed position, but only the amplitude of the induced voltage is varied. By so operating my control system it is noted the effects of extraneous voltages which may be induced in the pick-up coil V by thermocouple failure, for example. This latduced into the operation of the instrument. 10.

ter feature will be described-more in detail hereinafter.

When extraneous voltages are induced in the pick-up coil in the normal operating position of the latter, and the instrument is adjusted as it would necessarily have to be adjusted to be unresponsive to the currents produced by the extraneous voltages, a dead spot will be introextraneous voltages may be due to the presence of magnetic material .external to the field structure l8 which may cause distortion of the magnetic field or may be due to non-uniformity of the field structure itself. As will be readily appreciated it is extremely diflicult to construct a field structure in which the magnetic field will As will be apparent, when the pick-up coil I1- -is deflected in one direction from the position in which it is in zero inductive relation with the fundamental frequency of the alternating magnetic field set up in the field structure l8, a voltage of one phase will be induced in the pick-up coil to cause actuation of the relay 28 in one" direction and when the pick-up coil is deflected in the opposite direction a voltage of the opposite phase will be induced therein to cause actuation of the relay 28 in the opposite direction. If, however, transient induced voltages opposing either or both of the purposely induced voltages appear, the instrument will be prevented to the extent of the character and the magnitude of the transient voltage from effecting the desired actions of relay 28. If the transients are known and constant, theinstrument may be so adjusted as to compensate for them, but in any case must be made insensitive to them. Thus a "dead spot will be introduced into the \movement of the pick-up coil and the system will be rendered insensitive to a corresponding extent. I

Such a "dead spot is undesirable, however, in a controller of the type disclosed, and I prefer to so operate the system that the phase of the purposely induced voltage in the. pick-up coil does not change as the relay 28 is actuated from its open to its closed position, but only the amplitude of the induced voltage is changed. By adjusting the amplitude of the induced voltage in the pick-up coil, when the galvanometer moving coil is in its position .of electrical balance, to a value equal to or greater than the transient induced voltages in the pick-up coil, it will be apparent that the transient voltages will have no effect on the operation of the system. Or in other words, when the pick-up coil is normally in inductive relationship with the fundamental frequency of the alternating magnetic field set up in the field structure l8, the eflect of the transient voltages induced in the pick-up coil will be minimized and more stable operation of Such " system by the.

tive to minimize the effects of extraneous voltages induced in the pick-up coil l1.

14 is positive, and

control apparatus, occurring when the relay 28 is in its closed position that the apparatus shall "fail safe, that is any one of the failuresenumerated shall result in actuation of the relay 28 to its open position to thereby shut off the supply of heat to the furnace. Injury to the furnace and its contents which would ordinarily result before the attendant in charge would deby the arrangement illustrated in detail in Fig. 2.

sensitivity of the instrument may be soadjusted "that when the galvanometer moving coil is in its position of electrical balance the flow of cur-- rent through-the relay 28 will be insufficient to actuate the relay to closed position,-but on a slight change in temperature and consequent deflection of the galvanometer moving coil the energizing current to the relay will be increased sufliciently to actuate it to closed position.

This adjustment may conveniently be effected which-as shown includes a screw shaft H and an associated lever 12. One end of the lever 12 is rigid with a stud I3 which is mounted for rotation on the end of a horizontally projecting arm of a stationarybracket H, and the other end of the lever is adapted to slide in a groove on the screw shaft ll so that when the latter is rotated the tentiometric network 8 is balanced the relay 28 will be de-energized. Thus, when the g-alvanometer moving coil is de-energized, the relay 28 willrbe actuated to its open position if it is not already in this position and the supply of heat to the furnace will beshut .ofi. It is noted, however, that it is desirable in a system of this type to provide means for positively causing de-energization of the relay 28 upon thermocouple fail-' ure instead of relying solely on the normal adjustment of. the system. As mentioned hereinbefore, this end may be attained in my control same adjustment which is effec- For example, by adjusting the instrument so that when the temperature is at the desired value the galvanometermoving coil l4 will be slightly out of its mechanical zeroposition, that is, the

position which the galvanometer will assume when its terminals are shorted or opencircuited, it will be noted that thermocouple failure will result in movement of the galvanometer moving coil to its mechanical zero position. The pickup coil 11 may beso adjusted with respect to the .galvan'ometer moving coil. that in normal operation when the temperature is at the controlled value it will be slightly'in inductive relation with the field structure 18, the phase of the induced voltage .being such that a positive potential will be impressed on the control grid 33 of valve 29 during the halt cycles when the anode 35 of valve upon thermocouple burnout the resulting movement of the galvanometer moving coil into its position of mechanical zero adjustment will' rotate the pick-up coil l'l into zero inductive relation with the field structure l8, or into a position in which the voltage induced' therein will be of the opposite phase to thereby cause positive de-energization of the relay 28.

In accordance ith the second method of'opera-tion of my control system which I contemplate, the pick-up coil is normally maintained in a position of zero inductive relation with the field structure it and adapted to have voltages of opposite phases induced therein as it is deflected in one direction or the other from this normal position. It will be apparent that by providing a field structure l8 especially designed and magnetically shielded the transient voltages induced in the pick-up coil 11 may be minimized and consequently the dead spot referred to hereinbefore may be reduced to a minimum.

Thuawith either method of operation, the;

lever 12 will be rotated aboutits pivot thereby rotating the stud 13. A flexible U-shaped member 15 is rigidly connected at the end of one 7 arm to the end of a lever 16 the other end of which is rigid with the stud 13. The lever It extends back along the projecting arm of bracket 14 and, when the lever 12 is in a mid position along the screwshaft II, the lever 16 will bedirectly above and parallel to the projectingarm of the bracket, and is adapted to be moved oui of this parallel position when the screw shaft rotated. The flexible member 15 is so arranger with respect to the lever 16 that one arm is di-- rectly above and parallel to the latter and extends beyond the stud I3, and the otherarm is directly below and parallel to the lever 16. The galvanometer suspension wire is fixed to the latter arm of member 15 at a point which is on the axis of rotation of the stud so that when the screw shaft II is rotated the galvanometer moving coil J4 and the pilot coil I! will be rotated with respect to their respective field structures.

It is noted this galvanometer mechanical zero adjustment for adjusting the sensitivity and helping the instrument to fail safe may be facilitated when the milliammeter 64' is employed in conjunction therewith for indicating when the adjustment is at the desired value. For ex ample, by short circuiting the terminals of the galvanometer moving coil H, as by a switch 11,

the screw shaft 1| may be rotated until the anode current flow through valve 40 is a desirable value,

and by providing a milliammeter of suitable value, this current flow may desirably cause deflection of its pointer half way up scale. Movement of the galvanometer and pilot coil from this mechanically fixed position will then resultin the flow of more or less current through the milliam-' meter 64 and thereby in'deflection of its pointer in one direction or the other from the midposition.. Thus, by closing the switch 11, a rapid check may be made as to the mechanical zero ad- 'justment of the galvanometer and ii the adjustment is not correct, a correct adjustment may readily be effected by rotation of the screw shaft I I. As shown, a projection may desirably be provided in one end of the latter for facilitating the rotation thereof, as for example, by a suitabl key adapted to engage that projection.

v As was noted the pulsating anode current conducted by valve 10 is adapted to be controlled in accordance with the magnitude of the direct current potential maintained across resistor 60 and this potential in turn is adapted to be controlled in accordance with the magnitude of the alternating voltage impressed upon the input circuit of valve 29 by the pilot coil 11. Moreover, since the resistor 88 is shunted by the condenser 6|, it will become apparent that sudden changes in the alternating voltage induced in the pilot coil I1 will change only slightly the direct current potential drop' across resistor 68. Thus, if the galvanometer moving coil I4 and the pilot coil I1 are deflected from their neutral position as a result of jarring or vibration, the resulting transitory volt-age induced in the pilot coil I1 will produce only a slightchange in the direct current potential drop across resistor 80 which will or-- neutral positions and the relay armature will be permitted to assume its open position.

In Fig. 3 I have illustrated, more or less'diagrammatically, a modification-of the amplifier arrangement disclosed in Fig. l in which an additional stage of amplification is provided and in which the rectifier unit may be connected directly acrossthe supply conductors-L and L As illustrated the terminals of the pick-up coil I1 (not shown in this arrangement) are connected by conductors 25 and 26 to the input circuit of one triode section of an electronic valve 18 which may desirably be a twin amplifier type includ- 'ing two triodes in one envelope. This triode section includes ananode 18, a cathode 88, a heater filament 8|, and a control grid 82 and the output circuit thereof is resistance-capacity coupled by a resistance 83 and a condenser 83' to the input circuit of the second'triode section in-the envelope. For convenience in describing the circuit connections, the first mentioned triode will be referred to hereinafter as the triode A and the second mentioned triode will be referred to as the triode B.

The triode B includes an anode 84, a cathode 85, a heater filament 88, and a control grid 81. Energizing current is supplied the heater filaments 8| and 88 through a circuit which includes the heater filaments 8| and 85 of a twin type amplifier valve 88, and the heater filament 43 of.valve 48, and may be traced from the supply conductor L to the heater filaments 8| and 86, a conductor 81, heater filaments 8| and 85 of valve 88, a conductor. 88 in which a pair of resistors 88 and I08 are inserted, and the heater "filament 43 of valve 40 to the supply conductor L. The pairs of heater filaments 8| and 88, and 8| and 85, respectively, are illustrated as connected in parallel relation, but it will be readily I apparent these pairs of heater filaments may be connected in series relation, if desired, and, as illustrated, the heater filaments 8| and 88 are shunted by a suitable resistor 81.

Direct current anode ,voltage is supplied both triode sections of valve 18 through a circuit which utilizes the rectifying action of the anode 89 and cathode 88 of valve 88 and which may be traced from the supply conductor L to a conductor I8I, and the anode and cathode 88 of one triode section of valve auto one terminal of a condenser I82 which constitutes the positive side of a half wave rectifyingunit. The negative terminal of condenser I82 is connected by a conductor I83 to-the -supply conductor Lland, as will be apparent, the condenser I82 operates. to smooth outthe pulsations in the rectified current flow through the circuit including the anode 88 and cathode of valve 88 which impresses a definite constant voltag across its terminals.

As illustrated, the anode 18 of triode A is connected to the positive terminal of-condenser I02 through a resistor I83 and the cathode 88 is connected to the negative side thereof. Similarly,

the anode 84 of triode B is connected to the positive side of condenser I82 through a resistor I84 and the cathode 85 is connected to the negative terminal of the condenser. The flow of ripple current through both triode sections of valve 18 is limited to a negligibly. small value by operating the valve with the cathodes 88 and 85 virtually cold, the resistor 81 shunting the heater filaments 8| and 86 being provided for this purpose.

Itis noted that since individual electrically inanode 88 and cathode 88;

The output circuit of the triode B is resistance capacity coupled by a resistor I85 and a condenser I85 to the input circuit of the triode section of valve 88 which includes the anode 83. Anode voltage is supplied the latter mentioned triode section directly from the alternating current supply conductors L and L through a circuit which may be traced from thesupply conductor L, heater filament 43 of valve 48, a conductor I86 in which a resistor I81 is inserted, anode 83, and cathode 84 to the supply conductor L In order to smooth out the pulsating current fiow through resistor I 01 a condenser I88 of suitable value may desirably beconnected thereacross. Thus, when an alternating potential in phase with the supply line voltage is impressed on the input circuit of this triode section, the

potential drop across resistor I 81 will gradually increase in value until a condition of equilibrium is reached, and when an alternating potential out of phase with the supply line voltage is impressed on the input circuit of this triode, the potentialdrop across resistor I81 will gradually decrease in value.

Thus, a negative potential is built upon the anode 83 which is adapted to be varied as the pick-up coil I1 deflects in one direction or the other from its normally balanced position, and, as in the arrangement of Fig. 1, this negative potential is employed to control the conductivity of valve 48. vValve 48 is connected across the alternating supply conductors L and L in an in- -verted position with respect to the manner of connection of the triode section including anode 83 thereacross sothat the valve 48 will be conductive during theialternate half cycles when the triode sectionrferred to is non-conductive. As illustrated, the negative end ofresistor I81 is connected by a conductor I88 to the control grid 44 of valve 48 and the positive end of resistor I81 is connected through the heater filament 43 to the cathode 42.

Anode voltage is supplied the valve 48 througha circuit which may be traced from the supply conductor L, cathode 42, anode 4|, and a conductor 83, in which a relay 28 and: a milliam meter 64 are inserted, to the supply conductor L. The screen grid 45 is desirably maintained ment of Fig. 1, the valve is rendered conductive the 1 ductive relation is such as at a potential which is somewhat lower than the potential applied the anode 4| and as shown may be connected to'the point of connection of resistors 99 and I00.

Thus, in this arrangement, as in the arrange- 40 is adapted to be alternately rendered conductive and non-conductive and the amplitude of 'the pulsating current conducted thereby is adapted to be controlled in accordance with the direct current potential drop across resistor I01 which corresponds to the resistor 60 of Fig. l. 7

In Fig. 4, I have illustrated, more or less diagrammatically, a modification of a portion of the arrangement disclosed in Fig. l in which means are provided for modulating the heat input to the furnace I, that is, supplying heat at a steady rate to the furnace when the temperature is at the desired value and proportionately varying the supply of heat thereto in accordance with the extent of deviation of the temperature from the desired value. This end is obtained in this arrangement by providing feed back means for setting up an oscillation in the amplifier whereby the relay 28 will alternately be actuated to its open and closed pos'tion when the temperature is at the desired value, and as the temperature of the furnace deviates in one sense or the other from the desired value, the period of the oscillation will be varied proportionately so that the interval during which the relay is in its closed positionwill be varied with respect to the interval when it will be in its open poston. Thus, when the temperature is at the desired vme heat will be supplied the furnace at a predetermined rate, but as the temperature deviates-in one sense or the other from this value, the rate of heat supply will be correspondingly varied. This action will be readily distinguished from the action obtained with the arrangement of Figs. 1 and 3 in which on-off action is obtained, thatis, the heat supply to the furnace in the device of those figures is either entirely on or entirely off depending upon whether the temperature of the furnace is above or below the desired value.

Specifically, "a resistor conductor 63 29 and the milliammeter N, the negative end of resistor H beingc'onnected to one end of the relay 28 and the positive end beingconnected to the supply conductor L through the milliammeter 64. The cathode 3| of valve 29 is connected by a conductor Hi to a contact H2 which is in engagement with resistor H0. A resistor H3 isinserted in the conductor HI and a connection is provider. betweenthe cathode 3| and-the supply conductor L which includes a condenser H4. 1

- As will be readily apparent when the valve 40 current conducted by a potential drop across H0 is inserted in the this valve will produce in series relation with the relay,

of such magnitude as to permit the flow of sufficient current through valve 40 to actuatethe relay 28 to its closed position.

The resulting potential drop produced across resistor H0 by the flow of current conducted by valve 40 is in the direction to impress a positive potential on the control grid 33 of valve 29, which potential is superimposed on the alternating voltage impressed thereon by the pick-up coil l1, and causes an oscillation in the anode current conducted by valve 40 of suflicient magnitude to cause the relay 28 to be intermittently actuated to its open and closed position. As the voltage impressed on the input circuit of valve 29 by the pick-up coil l1 increases inone direction or the other, the magnitude of this oscillation is varied in such manner as to cause the relay to remainin its closed position for-a longer or shorter periodpf time with respect to the time in which it is in its open position.

For example, when the controlled temperature falls below the desired value, the voltage impressed on the input circuit of valve 29 by the pick-up coilll will become more and more pre-.

dominant over the voltage fed back by the resistor HI) until the latter is ineffective to cause opening of-the relay 28, and at intermediate values the feed back voltage will beefiective to cause the relay 28 to be opened for intervals of varying duration depending upon the extent of deviation ofthe controlled temperature from the desired value. When the temperature is. above the desired value thefeed back voltage and the voltageinduced by the pick-up coil will act in; r the same direction, that is, to cause opening of the relay 28, and in this case the feed back volt-. age wil be rendered more and more ineffective as the energizing current to the relay 28 is reduced, but the voltage induced in the pick-up coil will be sufficient to maintain the relay in its open position. At intermediate values the effect of the voltage induced in the pick-up coil to and adjustable along the resistor H0, a portion of which-depending upon the adjustment or contact I I2 along resistor H0,

is adapted to be fed back into the'input circuit of valve 29.

With this arrangementwhen the temperature of the furnace is at the desired value the pick-up coil II will be slightly in inductive relation with the-field structure l8 and the sense of this into impress a positive potential on the control'grid 33 of valve 29 durrnaintain'the relay continuously in open position will not be so pronounced and the relay will be actuated to its closed position for shorter and shorter intervals of time as the temperature of the furnace rises higher and higher above the control point. 'I'hus a proportioning action is obtained which operates to supply varying quantitles of heat to the furnace as the temperature deviates about. the controlled value.

In Figs. 5 and 6, I have illustrated, more or less diagrammatically, modifications of a portion of the arrangement disclosed Fig. 4 for obtain ving such proportional control of the supply of heating medium to the furnace I. As illustrated in Fig. 5 feed back means have been provided including a resistor H'll connected in the anode circuit ofvalve All, a connection between the cathode 3i of valve 29-and a contact H2 engaging and adjustable along the resistor H3, and a biasing resistor H5 connected between the cathode 3! and the supply conductor L The .con-

- nection referred to between the cathode 3| and ing the half cycles whenthe anode 35 of valve H 34 is positive." Thus, a negative potential will be impressed onlthecontrol grid 38 0t valve 34 which resultsin apotentialdrop across resistor the .contact H2 comprises a conductor III in which a resistor H9 shunted by a condenser H1- is inserted. The modification illustrated in Fig. 6 includes the resistor H0 and an associated resistor H3 and a condenser H8. As shown the cathode 3| of valve 29 is connected to the supplyconductor L and a connection is provided between the control grid 33 and resistor H0 including the pick-up coil, l1 (not shown in Fig.

6), a resistor H3'and a contact H2 engaging and adjustable along the resistor H0. Condenser H8 is connected between the left end of resistor H3, as seen in Fig. 6, and the supply conductor L j The operation of these modifications is similar to that of the Fig. 4 arrangement for causing an oscillation of the energizing current supplied relay 28 so that the latter will be intermittently actuated to its open and closed position, the

duration of the period in which it is-in its closed position with respect to the period in which it is in its open position being determined by the extent of deviation of the controlled temperature from the desired value.- I

While the modifications illustrated in Figs. 4-6 have been illustrated in connection with the amplifier arrangement disclosed in Fig. 1, it will be readily apparent to those skilled in the art that they may be adapted for use with the am- .plifler arrangement described in Fig, 3. For example, a resistor may be inserted in the conductor 63 between the relay 28 and the milliammeter 64 of this arrangement and a portion of th voltage drop thereacross may be fed back in the manner illustrated in Figs. 4-6 into the input circuit of the triode section of valve 18 which includes the anode l9.

While in accordance with the provisions. of the statutes, I-have illustrated and described the best form of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

Having now anode and cathode of said valve tending to maintain the anode voltage on said valve substantially constant and free from ripple tending to be produced therein by the fluctuations of said alternating voltage supply source, and auxiliary means associated with said electronic valve to minimize pulsations in the-current flow between the anode and cathode of said valve tending to be produced by ripple in said anode voltage including means for substantially increasing the impedance of the circuit path between the anode and cathode of said valve while maintaining the rectifying means, an electronic operating range of the grid voltage-plate current characteristic, over which said electronic valve is adapted to operate, over the portion of said characteristic having the maximum slope.-

2. Means for amplifying an alternating voltage including an alternating voltage supply source,

anode, a cathode and a control electrode, means to'apply said alternating voltage supply source between the anode and cathode of said valve through said rectifying means, means to apply said alternating voltage to be amplified between the cathode and control electrode of said valve,

filtering means connected between the anode and ing direct current and described my invention, what I claim as new and desire to secure by Letters Patcathode of said valve tending to maintain the anode voltage on saidvv valve substantially constant and free from ripple tending to be produced therein by the fluctuations of said alternating voltage supply source, and auxiliary means associated with said electronic valve to minimize pulsations in the current fiow between the anode and cathode of said valvetending to be produced by ripple in said anode voltage including means for substantially increasing the anode to cathode impedance of said valve without varying the potential of said control electrode relatively to the potential of said cathode.

3. In combination, an amplifier comprising an electronic device having an anode, a cathode and a control electrode, means for energizing said electronic device comprising a source of fluctuatfiltering means connected between the anode and cathode of said device, and auxiliary means associated with said device to minimize pulsations in the current flow between the anode and cathode of said device tending to be produced by thefluctuations in said direct current source including means to increase the impedance of the circuit path between the anode and cathode of said valve while maintaining the operating range of the grid voltage plate current characteristic, over which said electronic device is adapted to operate, over the portion of said characteristic having the maximum slope.

4. vIn combination, an amplifier comprising an electronic device having an anode, a cathode and a control electrode, means for energizing said electronic device comprising a source of fluctuating direct current and filtering means connected between the anode and cathode of said device, and auxiliary means associated with said device to minimize pulsations in the current flow between the anode and cathode of said device tending to be produced by the fluctuations in said direct current source including means for increasing the impedance of the circuit path between the anode and cathode of said device without varying the potential of said control electrode relatively to the potential of said cathode.

WALTER P. WILLS.

valve having an 

